Avionics Expert - A 911
Remote Control Lesson
For Popular Mechanics
From Jon Carlson

carlson.jon@att.net
3-16-5

In response to the article
on the photo showing odd shapes on the bottom of the airliner that struck
the South Tower, an Avionics expert has a RC lesson for Popular Mechanics
and all of us.

Excerpts from his emails:

I have 35 years experience in this area of Avionics on
numerous military and commercial

aircraft.

I took the first digital avionic system aircraft to the
field in 1969 and have worked on numerous military aircraft, and studied
the architecture on just about all commercial air-carriers over the last
30 some years.

Instrumentation packages added to aircraft to augment
control or take over automatic flight control are old hat.

The package shown on your photo is evidently a receiver
and the associated electronics required to replace the AFCS package (Auto
Pilot and Stability Control Unit).

The two blade antenna (CIRCLED IN YELLOW) are not normal
(Their reflections makes it looks like a last minute add on.) for this
type plane. They are VHF (too large for UHF) antennas used to control
the replacement autopilot package.

This looks like a remote control package on this aircraft.
What you are looking at is not the normal configuration of a commercial
aircraft.

In UAV applications, signal bounce off the earth or buildings
may induce fading, causing signal breakup. DTC is reknowned for its line
of true diversity receivers, using spatial diversity to overcome fades
and multipath. Pairs of receivers and antennas tuned to the same frequency
are used to receive a single transmitted signal. A proprietary voting logic
board votes to the best signal during the horizontal retrace, over 15,000
times per second. This greatly enhances video quality.

DTC's miniature microwave video transmitters <video-transmitter-250mw.html>
and receivers are well suited for UAV downlinks, transmitting one channel
of video and up to two telemetry channels over audio subcarriers